This invention relates to motor vehicle brake drums that comprise a stamped steel drum back, cast iron braking surface with the balance of the drum composed of die cast aluminum or other light weight alloy.
Fuel economy improvements demand size and weight reduction of motor vehicle components while often at the same time requiring improved structural properties. It is known that die casting with light metal as with aluminum alloy can replace some features in brake drums to reduce weight. In this invention, however, a steel drum back is used that allows weight reduction compared to structurally similar drums with cast aluminum drum backs.
The commercially acceptable brake drums of this invention have a steel drum back and cast iron braking ring surrounded by an aluminum die cast barrel that blend advantage of the weight reduction afforded by light weight die cast with performance, cost and weight advantages derived from a steel drum back and cast iron braking ring. For example, the steel drum back requires less machining than a comparable die cast drum back as well as having better brake roughness ratings. Further, use of die casting of the drum barrel permits lower weight and other advantages such as high productivity and inherently better centering of the drum back and braking ring which reduce the amount of balancing required. Even further, the braking ring with its rough outer surface has superior heat transfer properties over a braking ring with alternative surfaces (i.e., smooth, as cast or locking lugs) while facilitating processing as it eliminates need for complex chucking during its machining.
It is an object of this invention to provide brake drums of reduced weight without requiring increase of wheel tread dimensions.
It is an object of this invention to provide brake drums that are conveniently processed and of reduced cost.
It is an object of this invention to provide a brake drum that is readily balanced with conventional welding techniques.
It is an object of this invention to provide a brake drum that does not require unique axle flange attachment and can be conveniently removed from the shaft for servicing.
It is an object of this invention to provide a composite brake drum using a substantially bi-planar stamped steel drum back for desirable brake roughness ratings.
These and other objects are accomplished according to the hereinafter invention.